Well, they might go on an adventure to discover new jutsus. Sasuke could be on a mission to learn more about his clan's secrets and takes Naruto along for the ride because he knows Naruto's strength. Maybe they'll encounter powerful enemies and have to rely on each other to survive.
One reason could be for power. Combining their strengths through marriage could make them an even more formidable force. Maybe Sasuke saw it as a strategic move to protect their village or to face some greater threat that they are not aware of yet.
In some cases, Sasuke could be angry. He might see Naruto's request as a sign of weakness or as Naruto giving up too easily. He could lash out at Naruto, telling him to fight instead of asking for death. However, he would still be deeply troubled by the request and would probably struggle with it for a long time, constantly thinking about whether or not he should consider it.
Sasuke's reaction could be complex. At first, he would be enraged. After all, the Rinnegan is a symbol of his power and his journey to gain strength. However, he might also have some mixed feelings. He and Naruto have a deep bond, and he might wonder if Naruto had a good reason for taking it. But overall, his initial reaction would likely be one of fury and a desire to get his power back.
One possible plotline could be that Naruto gets seriously injured during a mission. Sasuke and Sakura, with their combined skills, take him in and nurse him back to health. They might have to deal with Naruto's stubbornness when it comes to resting and following medical advice. Sakura could use her medical knowledge, while Sasuke could provide protection and also train Naruto in new techniques once he's recovered a bit, strengthening their bond as friends.
There could be moments of frustration for Naruto, especially when Sasuke is fussy or won't do what Naruto wants him to. But Naruto's love for Sasuke would override that. Emotionally, Naruto would be pouring all his love into taking care of Sasuke, trying to give him the family he never had. And Sasuke, even as a baby, might show signs of his future strong - willed self, which could both amuse and challenge Naruto.
Well, it could lead to a major shift in the power balance among the characters. Sasuke would be weakened without his Rinnegan, and Naruto would have to deal with the new power. There might also be some internal conflict within Naruto as he tries to come to terms with using Sasuke's power. Maybe he would feel guilty at first, but then realize it's for the greater good. Also, other characters like Kakashi or Sakura might have different reactions. Kakashi could be worried about Naruto being corrupted by the power, while Sakura might be more concerned about Sasuke's well - being without his most powerful ability.
Well, in some fanfictions, Naruto might use his shadow clones to search every possible location. Once he locates Sasuke, he could use his strong bond and persuasion skills to convince Sasuke to come with him. Naruto might remind Sasuke of their past friendship and the dreams they once shared, like protecting the village together.
One reason could be that Sasuke realizes he needs Naruto's unique abilities. Naruto has the Nine - Tails' power which could be useful in a certain task. So he takes Naruto with him to achieve a common goal.
They might go on a journey to discover the secrets of Itachi's past. Naruto could learn a lot from Itachi about the Uchiha clan and their powers. Maybe they'll encounter other powerful ninja clans along the way and have to fight or make alliances.